Magnitude (astronomy)

magnitudemagnitudesmagabsolute magnitude magnitudeastronomical magnitudeapparent magnitudeastronomical magnitude systembrighterbrightness
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths.wikipedia
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Extinction (astronomy)

extinctionextinction factorinterstellar extinction
Apparent magnitude depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness.
For stars that lie near the plane of the Milky Way and are within a few thousand parsecs of the Earth, extinction in the visual band of frequencies (photometric system) is roughly 1.8 magnitudes per kiloparsec.

Luminosity

luminousbolometric luminosityluminosities
Apparent magnitude depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness.
Luminosity can also be given in terms of the astronomical magnitude system: the absolute bolometric magnitude (M bol ) of an object is a logarithmic measure of its total energy emission rate, while absolute magnitude is a logarithmic measure of the luminosity within some specific wavelength range or filter band.

List of brightest stars

brightest starsbrightest starone of the brightest stars
Stars that have magnitudes between 1.5 and 2.5 are called second-magnitude; there are some 20 stars brighter than 1.5, which are first-magnitude stars (see the list of brightest stars).
This is a list of stars down to magnitude +2.50, as determined by their maximum, total, or combined visual magnitudes as viewed from Earth.

Galileo Galilei

GalileoGalileanGalilei
Astronomers from Galileo to Jaques Cassini mistook these spurious disks for the physical bodies of stars, and thus into the eighteenth century continued to think of magnitude in terms of the physical size of a star.
(In fact, it is not possible to observe the physical size of distant stars without modern telescopes).

Arcturus

ArcturiansArcturianAlpha Boo
To the unaided eye, a more prominent star such as Sirius or Arcturus appears larger than a less prominent star such as Mizar, which in turn appears larger than a truly faint star such as Alcor. For example, Sirius is magnitude −1.46, Arcturus is −0.04, Aldebaran is 0.85, Spica is 1.04, and Procyon is 0.34.
With a near-infrared J band magnitude of −2.2, only Betelgeuse (−2.9) and R Doradus (−2.6) are brighter.

Magnitude

Magnitude (disambiguation)
The magnitude system dates back roughly 2000 years to the Greek astronomer Hipparchus (or the Alexandrian astronomer Ptolemy—references vary) who classified stars by their apparent brightness, which they saw as size (magnitude means "bigness, size" ).

Absolute magnitude

Hbolometric magnitudeabsolute magnitude (H)
Astronomers use two different definitions of magnitude: apparent magnitude and absolute magnitude.
Absolute magnitude (M) is a measure of the luminosity of a celestial object, on an inverse logarithmic astronomical magnitude scale.

Aldebaran

Alpha Tauribrightest starRohini
For example, Sirius is magnitude −1.46, Arcturus is −0.04, Aldebaran is 0.85, Spica is 1.04, and Procyon is 0.34.
With a near-infrared J band magnitude of −2.1, only Betelgeuse (−2.9), R Doradus (−2.6), and Arcturus (−2.2) are brighter at that wavelength.

Betelgeuse

Alpha OrionisBételgeuseα Ori
Betelgeuse is the brightest near-infrared source in the sky with a J band magnitude of −2.99.

Distance modulus

:This is known as the distance modulus, where d is the distance to the star measured in parsecs, m is the apparent magnitude, and M is the absolute magnitude.
It describes distances on a logarithmic scale based on the astronomical magnitude system.

N. R. Pogson

Norman Robert PogsonNorman PogsonN.R. Pogson
Thus in 1856 Norman Pogson of Oxford proposed that a logarithmic scale of 5√100 ≈ 2.512 be adopted between magnitudes, so five magnitude steps corresponded precisely to a factor of 100 in brightness.
He introduced a mathematical scale of stellar magnitudes with the ratio of two successive magnitudes being the fifth root of one hundred (~2.512) and referred to as Pogson's ratio.

AB magnitude

AB system
Current absolute reference systems include the AB magnitude system, in which the reference is a source with a constant flux density per unit frequency, and the STMAG system, in which the reference source is instead defined to have constant flux density per unit wavelength.
The AB magnitude system is an astronomical magnitude system.

Apparent magnitude

apparent visual magnitudemagnitudevisual magnitude
Astronomers use two different definitions of magnitude: apparent magnitude and absolute magnitude. For example, the human eye is more sensitive to yellow and red light than to blue, and photographic film more to blue than to yellow/red, giving different values of visual magnitude and photographic magnitude.
The brighter an object is, the lower its magnitude.

Intensity (physics)

intensityintensitieslight intensity
Under the modern logarithmic magnitude scale, two objects, one of which is used as a reference or baseline, whose intensities (brightnesses) measured from Earth in units of power per unit area (such as watts per square metre, W m −2 ) are

Photographic magnitude

For example, the human eye is more sensitive to yellow and red light than to blue, and photographic film more to blue than to yellow/red, giving different values of visual magnitude and photographic magnitude.

Astronomy

astronomicalastronomerastronomers
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths.

Dimensionless quantity

dimensionlessdimensionless numberdimensionless quantities
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths.

Brightness

brightintensitybrilliant
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths.

Passband

pass bandpass-bandpassband signal
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths.

Visible spectrum

visiblevisible lightspectrum
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths.

Infrared

IRnear-infraredinfra-red
In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths.

Hipparchus

HipparchosHipparchus of NicaeaHipparchus of Nicea
The magnitude system dates back roughly 2000 years to the Greek astronomer Hipparchus (or the Alexandrian astronomer Ptolemy—references vary) who classified stars by their apparent brightness, which they saw as size (magnitude means "bigness, size" ). An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus.

Logarithmic scale

logarithmiclogarithmic unitLog
The scale is logarithmic and defined such that each step of one magnitude changes the brightness by a factor of the fifth root of 100, or approximately 2.512.

Nth root

radicalsn''th rootroot
The scale is logarithmic and defined such that each step of one magnitude changes the brightness by a factor of the fifth root of 100, or approximately 2.512.

Night sky

night skiessky''' of the Earthsky of Earth
The apparent magnitude (m) is the brightness of an object as it appears in the night sky from Earth.